Mm, I don't like the Chart TimeFrame part, I always change timeframes 😄
By the way, you should not have problems when you put the same EA on different pairs, because all the blocks are set up (by default) to work only with the Current pair. Even if the magic number is the same in two trades, EURUSD and EURAUD, only because the EA is working on EURAUD should not touch EURUSD at all. Again, this is the behavior by default, it can be changed!
The only problem that I can imagine is when we want to put the same EA on two charts from the same pair, but with different magic numbers. In this case the problem can be that we can forget to change the MagicStart for one of both EAs. But if there are 2 EAs, like EA1 and EA2, then both will be unique.